Coronal section of right temporal bone. (Mastoid cells labeled at bottom left.)
MRI showing fluid in mastoid air cells
At the upper and front part of the process they are large and irregular and contain air (a form of skeletal pneumaticity), but toward the lower part they diminish in size, while those at the apex of the process are frequently quite small and contain marrow; occasionally they are entirely absent, and the mastoid is then solid throughout.
At birth the mastoid is not pneumatized, but becomes aerated over the first year of life. Poor pneumatization is associated with eustachian tube dysfunction.
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- Anatomy image: hn1-8 at the College of Medicine at SUNY Upstate Medical University